This invention relates to a cooling system for a supercharged internal-combustion engine for the two-stage cooling of the charge air compressed by an exhaust gas turbocharger.
More specifically, a cooling system is known, for example, from the German Patent Document DE-B-15 76 718, having a high-temperature circulating system which, in a main branch, comprises the internal-combustion engine and a high-temperature recooler and, in a secondary branch, comprises a high-temperature charge air cooler. The coolant required for the secondary branch is taken from the main branch and, after flowing through the high-temperature charge air cooler, is admixed to a coolant flow flowing away from the high-temperature recooler which leads to the coolant inlet of the internal-combustion engine. The system also has a low-temperature circulating system comprising a low-temperature recooler and a low-temperature charge air cooler connected in series with it, through which the charge air, which flows out of the high-temperature charge air cooler, flows for a further cooling before the charge air is fed to the cylinders of the internal-combustion engine. The system also has coolant pumps for the circulating of the coolant.
For the cooling of the charge air in two stages, according to the German Patent Document DE-B-15 76 718, two charge air coolers are used through which coolant flows that has different temperature levels. The two charge air coolers are assigned to two separate coolant circulating systems--a high-temperature circulating system and a low-temperature circulating system. The high-temperature circulating system comprises a main branch with the internal-combustion engine and a high-temperature recooler. The charge air cooler which cools the charge air in a first stage is situated in a secondary branch of the high-temperature circulating system. The coolant required in the secondary branch is taken from the coolant flow leaving the internal-combustion engine and is guided to the charge air cooler in the secondary branch. The coolant flowing out of the charge air cooler is admixed to the coolant flow leaving the high-temperature recooler which leads to the coolant inlet of the internal-combustion engine. The low-temperature circulating system comprises a low-temperature recooler and connected in series with respect to it, the charge air cooler for the cooling of the charge air in a second stage. The cooling of the engine lubricating oil takes place via a heat exchanger which is also arranged in the low-temperature circulating system. By means of the cooling system with a high-temperature circulating system and a low-temperature circulating system, an intensive cooling of the charge air is permitted in order to increase the power of the internal-combustion engine. It is a disadvantage of the indicated cooling system that the coolant quantity guided to the secondary branch is branched off from the coolant flow leaving the internal-combustion engine which has a relatively high temperature level. Because of the high temperature level of the coolant, the cooling of the charge air is correspondingly limited in the first stage. In addition, the total coolant quantity circulating in the high-temperature circulating system is large because only a portion of it flows through the high-temperature recooler.
In the British Patent Document GB-A-20 57 764, another cooling system is illustrated having a high-temperature and a low-temperature circulating system for the two-stage cooling of the charge air in two charge air coolers. The cooling system differs from the above-described cooling system only because of the fact that the coolant which flows off in the secondary branch of the high-temperature circulating system from the charge air cooler is admixed to the coolant flow leaving the internal-combustion engine which leads to the coolant inlet of the high-temperature recooler. The coolant required in the secondary branch is branched off the coolant flow leaving the high-temperature recooler. In this case, it is also disadvantageous that the required total coolant quantity is large because only a portion of the circulating coolant is used for the cooling of the internal-combustion engine. Because of the relatively low temperature level of the coolant flows mixed in front of the coolant inlet of the high-temperature recooler, the possible cooler capacity is not optimally utilized. Therefore, the overall volume of the cooler is large.
In a variant of the cooling system according to the British Patent Document GB-A-20 57 564, the coolant flow leaving the charge air cooler of the low-temperature circulating system is also admixed to the coolant flow guided to the high-temperature recooler. The coolant required in the low-temperature circulating system, like the coolant required for the secondary branch of the high-temperature circulating system, is branched off the coolant flow leaving the high-temperature recooler and is then guided via the low-temperature recooler before it enters into the low-temperature charge air cooler. In this case, only one coolant pump is required. Other disadvantages in this case are the fact that the total coolant requirement, because of the mixing of the coolant flows behind the internal-combustion engine, is relatively high and the fact that the capacity of the high-temperature recooler is not optimally utilized. Because of the series connection of the high-temperature recooler and the low-temperature recooler, a high flow resistance is obtained necessitating the use of a pump having a high power consumption. A complicated pipe arrangement is also necessary in this case.
There is therefore needed a cooling system for a supercharged internal-combustion engine which is simple with respect to the arrangement of the pipes, requires a low total quantity of coolant, and optimally utilizes the capacity of the recoolers.
These needs are met in the present invention by a cooling system for a supercharged internal-combustion engine having a high-temperature circulating system which, in a main branch, comprises the internal-combustion engine and a high-temperature recooler and, in a secondary branch, comprises a high-temperature charge air cooler. The coolant required for the secondary branch is taken from the main branch and, after flowing through the high-temperature charge air cooler, is admixed to a coolant flow flowing away from the high-temperature recooler which leads to the coolant inlet of the internal-combustion engine. The system also has a low-temperature circulating system comprising a low-temperature recooler and a low-temperature charge air cooler connected in series with it, through which the charge air, which flows out of the high-temperature charge air cooler, flows for a further cooling before the charge air is fed to the cylinders of the internal-combustion engine. The system also has coolant pumps for the circulating of the coolant. The coolant required in the secondary branch is branched off from the coolant flow leaving the high-temperature recooler. The coolant flowing through the internal-combustion engine subsequently flows to the high-temperature recooler. Alternately, the coolant required in the secondary branch is branched off a coolant flow, in which the total quantity of the coolant leaving the high-temperature recooler and the coolant flowing out of the secondary branch from the high-temperature charge air cooler are mixed. The coolant flowing through the internal-combustion engine then flows to the high-temperature recooler.
As noted above, in the present invention, the coolant quantity, which flows in the secondary branch away from the high-temperature charge air cooler, is admixed to the coolant quantity flowing in the main circulating system from the high-temperature recooler to the internal-combustion engine, and the same quantity of coolant, which flows through the high-temperature recooler, is also guided to the coolant inlet of the internal-combustion engine. Thus, the largest possible coolant quantity, in each case, participates in the heat exchange in the internal-combustion engine and in the high-temperature recooler, and the required total coolant quantity can therefore be kept low. Because of the higher temperature level of the coolant entering into the high-temperature recooler, the total degree of exchange of the high-temperature recooler will rise and is therefore optimally utilized.
The construction of the cooling system is simplified with respect to the arrangement of the pipes because, in this case, no pipe has to lead from the internal-combustion engine to the high-temperature charge air cooler in the high-temperature circulating system. However, the cooling of the charge air that is possible in the high-temperature charge air cooler is slightly reduced because of the higher coolant temperature.
In the cooling system, the coolant flows of the high-temperature and the low-temperature circulating systems are mixed. Specifically, the coolant flow which leaves the low-temperature charge air cooler (as well as the heat exchanger for engine oil and gear lubricant oil possibly connected behind it) is admixed to the mixture of the coolant flows of the high-temperature circulating system. From this mixed flow, the coolant quantity required in the secondary branch of the high-temperature circulating system as well as the coolant quantity which is guided to the coolant inlet of the low-temperature recooler is taken. It is advantageous that a more simplified arrangement of the pipes is obtained and, in addition, only one coolant pump is required. Also, the efficiency of the low-temperature recooler can be increased.
According to the present invention, it is also expedient to arrange the heat exchangers for the engine oil and the gear lubricant oil in the low-temperature circulating system. When the oil type is selected, the temperature level of the high-temperature circulating system therefore does not have to be taken into account. For a fast, load-dependent control of the coolant flow through the low-temperature charge air cooler, a control element with a bypass is provided in order to be able to achieve corresponding charge air temperatures in the case of fast load changes. The control element can be influenced by means of the control rod path, the rotational speed of the charger, the charge air pressure or the temperature of the coolant leaving the high-temperature recooler.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.